There presently exist many system applications wherein precise information regarding the head position of an operator is required for efficient operation. Examples of such applications are fire control systems for high performance aircraft employing helmet mounted displays wherein it is necessary to correlate target information with accurate head position information in order to properly display target information on the helmet display.
Other applications include positioning of weapons, visual field orientation for simulators, clinical head movement monitors, robotics and remote piloted vehicle orientation.
Head position indication devices presently exist in the form of binocular matching systems, electromagnetic phase-tracking systems and mechanical axis pickoffs. The first two types are quite expensive and complicated while the mechanical axis pickoffs interfere with free head movement of the operator.
Further examples of existing systems are as follows:
An electro-optical head position sensing system developed by CAE Electronics, Montreal, Canada which implements two detectors. Although detailed information is not available it appears that the system does not achieve the resolution and accuracy of the present system. (Ref: Fischetti. Truxal: "Simulating the Right Stuff"-IEEE Spectrum, March 1985).
A magnetic head position sensor has been developed by Polhemus for McDonald-Douglas. This system is sensitive to electromagnetic disturbances and changes in position of ferromagnetic objects. There are also problems in linearity and calibration. (Ref: "Operating and Maintenance Manual for the Vcass/Ahms System"-OMM-80-1018-1-8 Apr. 80, Polhemus Navigation Sciences Inc.).
An electro-optical system by Selspot AB, Sweden implements two detectors . This system is only useful for relatively large distances from the sensed object. It is sensitive to optical disturbances and therefor only useful indoors.